A cancer vaccine that shows tremendous promise for the treatment of prostate cancer is the PROSTVAC-VF vector-based vaccine. The vaccine is composed of an initial vaccination with a recombinant vaccinia virus containing the human genes for prostate specific antigen (PSA) and three costimulatory molecules (B7.1, LFA-3, and ICAM-1), followed by booster injections with a fowlpox virus with the same four transgenes (see, e.g., Garnett et al., Curr. Pharm. Des., 12: 351-361 (2006), and Madan et al., Expert Opin. Biol. Ther., 10: 19-28 (2010)). The vaccine is designed to stimulate an immune response to prostate tumor cells that express high levels of PSA. The vaccine has been evaluated in several phase I and phase II clinical trials with excellent results (see, e.g., Lechleider et al., Clin. Cancer Res., 14: 5284-5291 (2008), Madan et al., Clin. Cancer Res., 14: 4526-4531 (2008), Garnett et al., Clin. Cancer Res., 14: 3536-3544 (2008), Arlen et al., J. Urol., 178: 1515-1520 (2007), Theoret et al., Clin. Genitourin. Cancer, 5: 347-350 (2007), and Arlen et al., Clin. Cancer Res., 12: 1260-1269 (2006)).